First published online October 24, 2002; 10.1104/pp.008185
Plant Physiol, November 2002, Vol. 130, pp. 1552-1561
Mechanisms of Arsenic Hyperaccumulation in Pteris
vittata. Uptake Kinetics, Interactions with Phosphate, and
Arsenic Speciation1
Junru
Wang,2
Fang-Jie
Zhao,*
Andrew A.
Meharg,
Andrea
Raab,
Joerg
Feldmann, and
Steve P.
McGrath
Agriculture and Environment Division, Rothamsted Research,
Harpenden, Hertfordshire AL5 2JQ, United Kingdom (J.W., F.-J.Z.,
S.P.M.); and School of Biological Sciences (A.A.M.) and Chemistry
(A.R., J.F.), University of Aberdeen, Aberdeen AB24 3UU, United
Kingdom
The mechanisms of arsenic (As) hyperaccumulation in
Pteris vittata, the first identified As
hyperaccumulator, are unknown. We investigated the interactions of
arsenate and phosphate on the uptake and distribution of As and
phosphorus (P), and As speciation in P. vittata. In an
18-d hydroponic experiment with varying concentrations of arsenate and
phosphate, P. vittata accumulated As in the fronds up to
27,000 mg As kg 1 dry weight, and the frond As to root As
concentration ratio varied between 1.3 and 6.7. Increasing phosphate
supply decreased As uptake markedly, with the effect being greater on
root As concentration than on shoot As concentration. Increasing
arsenate supply decreased the P concentration in the roots, but not in
the fronds. Presence of phosphate in the uptake solution decreased
arsenate influx markedly, whereas P starvation for 8 d increased
the maximum net influx by 2.5-fold. The rate of arsenite uptake was
10% of that for arsenate in the absence of phosphate. Neither P
starvation nor the presence of phosphate affected arsenite uptake.
Within 8 h, 50% to 78% of the As taken up was distributed to the
fronds, with a higher translocation efficiency for arsenite than for
arsenate. In fronds, 49% to 94% of the As was extracted with a
phosphate buffer (pH 5.6). Speciation analysis using high-performance
liquid chromatography-inductively coupled plasma mass spectroscopy
showed that >85% of the extracted As was in the form of arsenite, and the remaining mostly as arsenate. We conclude that arsenate is taken up
by P. vittata via the phosphate transporters, reduced to
arsenite, and sequestered in the fronds primarily as As(III).
1
This work was supported by the Biotechnology and
Biological Sciences Research Council of the UK (grant to Rothamsted Research).
2
Present address: Life Science College,
Northwest Sci-Tech University of Agriculture and Forestry, Yangling,
Shaanxi 712100, China.
*
Corresponding author; e-mail Fangjie.Zhao{at}bbsrc.ac.uk; fax
44-1582-760981.
© 2002 American Society of Plant Biologists
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